Persistent hole reservation

ABSTRACT

Techniques are provided for persistent hole reservation. For example, hole reservation flags of operations targeting a first storage object of a first node are replicated into replication operations targeting a second storage object of a second node during a transition operation to transition the first storage object and the second storage object from an asynchronous replication state to a synchronous replication state. In another example, the second storage object is grown to a size of a replication punch hole operation that failed due to targeting a file block number greater than an end of size of the second storage object.

BACKGROUND

Many storage environments provide synchronous replication whereoperations targeting a first storage object are replicated to a secondstorage object that may be maintained as a replicated backup of thefirst storage object. For example, an operation targeting the firststorage object may be received by a first node that stores the firststorage object. The operation is “split” to create a replicationoperation that is a replication of the operation. The operation and thereplication operation are synchronously replicated, such as by locallyexecuting the operation upon the first storage object by the first nodeand transmitting the replication operation to the second node forexecution (e.g., parallel execution) upon the second storage object. Anacknowledgment of success of the operation is transmitted back to aclient that generated the operation based upon both the operation andthe replication operation being acknowledged by the first node and thesecond node.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a component block diagram illustrating an example clusterednetwork in which an embodiment of the invention may be implemented.

FIG. 2 is a component block diagram illustrating an example data storagesystem in which an embodiment of the invention may be implemented.

FIG. 3 is a flow chart illustrating an example method for timestampconsistency.

FIG. 4A is a component block diagram illustrating an example system fortimestamp consistency, where timestamp consistency is provided for anoperation and a replication operation.

FIG. 4B is a component block diagram illustrating an example system fortimestamp consistency, where selective replication of operations isperformed based upon whether the operations result in on-diskmodifications.

FIG. 4C is a component block diagram illustrating an example system fortimestamp consistency, where sequential replication of operations withan fpolicy flag is performed.

FIG. 5 is a flow chart illustrating an example method for inofilemanagement.

FIG. 6A is a component block diagram illustrating an example system forinofile management, where a size of an inofile is increased.

FIG. 6B is a component block diagram illustrating an example system forinofile management, where a size of an inofile is not increased.

FIG. 6C is a component block diagram illustrating an example system forinofile management, where access control list file handle parity isprovided.

FIG. 7 is a flow chart illustrating an example method for freeing andutilizing unused inodes.

FIG. 8 is a component block diagram illustrating an example systemfreeing and utilizing unused inodes.

FIG. 9 is a flow chart illustrating an example method for holepreservation.

FIG. 10A is a component block diagram illustrating an example system forhole preservation, where hole reservation flags are replicated.

FIG. 10B is a component block diagram illustrating an example system forhole preservation, where a write operation is used to grow a storageobject.

FIG. 11 is an example of a computer readable medium in which anembodiment of the invention may be implemented.

FIG. 12 is a component block diagram illustrating an example computingenvironment in which an embodiment of the invention may be implemented.

DETAILED DESCRIPTION

Some examples of the claimed subject matter are now described withreference to the drawings, where like reference numerals are generallyused to refer to like elements throughout. In the following description,for purposes of explanation, numerous specific details are set forth inorder to provide an understanding of the claimed subject matter. It maybe evident, however, that the claimed subject matter may be practicedwithout these specific details. Nothing in this detailed description isadmitted as prior art.

The methods and systems provided herein improve replication, such assynchronous replication techniques. Synchronous replication can beimplemented as a zero recovery point objective (RPO) replication enginethat can provide zero data loss in the event a node fails in a computingenvironment. This is achieved by intercepting I/O targeting a firststorage object (e.g., a first volume, file, directory, storage virtualmachine, logical unit number (LUN), etc.) and replicating (splitting)the I/O to create replicated I/O that is executed (synchronouslyreplicated) upon a second storage object that is maintained as a replicaof the first storage object. Parallel splitting is performed where anoperation is dispatched to both a first node hosting the first storageobject and a second node hosting the second storage node in parallel.This reduces latency compared to merely sequentially splittingoperations where a replication operation is dispatched to the secondnode only after completion of a corresponding operation by the firstnode.

A quick reconciliation (quick reconcile) can be performed if a parallelsplit replication operation succeeded at the second node but acorresponding operation fails at the first node. The quickreconciliation will undo the replication operation at the second nodeusing old data from the first node before responding with a failure. Inthis way, the first storage object and the second storage object will beconsistent in that they both will comprise the same old data. A failuremessage is returned to the client device because the operation and thereplication operation were not fully executed and committed to write thenew data to the first storage object and the second storage object.Issues can arise when performing the quick reconciliation, such as wherethe second node loses a hole reservation flag due to data being writtento the second storage object during the quick reconciliation.Accordingly, as will be described in further detail, hole reservationflags at the first node are conveyed to the second node during the quickreconciliation.

A transition operation can be performed to provide non-disruptivere-synchronization between the first node and the second node. Thetransition operation uses a dirty region log to track dirty regions ofthe first storage object modified by data operations such as Writeduring the transition phase and a metadata log to track metadataoperations executed during the transition phase. Dirty data (e.g.,modified data of the first storage object not yet replicated to thesecond storage object) as identified by the dirty region log andmetadata operations as logged by the metadata log are applied to thesecond node to bring the first storage object and the second storageobject into a synchronous replication relationship. Metadata operationsare first replicated from the metadata log, and then the dirty data isreplicated. Issues can arise during the transition operation becauseoperations (e.g., dirty data) may not be replicated to the second nodeaccording to the order executed upon the first node, and that the dirtyregion log lacks details about which flags, such as a hole reservationflag, were part of which write operations that created the dirty data.Accordingly, as will be described in further detail, hole reservationflags are replicated to the second node during the transition operationin order to preserve persistent hole reservations.

In an embodiment, timestamp consistency is provided between the firstnode and the second node during parallel splitting of operations.Replicating the timestamp information to the second node in a consistentmatter is useful because the timestamp information can be used by thesecond node to perform data integrity validation, incremental backups,etc. A splitter component is configured to intercept operations beforesuch operations reach a file system or operating system of the firstnode. The splitter component is configured to split (replicate) anoperation to create a replication operation. Generally, a timestamp isassigned using a get time of day function when the operation is executedin order to set an mtime and/or ctime of storage objects modified by theoperation. However, with parallel splitting, the second node will notknow what time the first node used. Accordingly, the splitter componentassigns a same timestamp to both the operation and the replicationoperation so that the same timestamp value is used by both the firstnode and the second node. The operation and the replication operationare executed on the storage objects on the first node and the secondnode. If the timestamp assigned to the replication operation is largerthan a current timestamp of the second storage object, then thetimestamp is assigned as a new current timestamp for the second storageobject (otherwise the timestamp is not assigned). If the timestampassigned to the operation is larger than a current timestamp of thefirst storage object, then the timestamp from the operation is assignedas a new current timestamp for the first storage object (otherwise thetimestamp is not assigned).

In an embodiment, an inofile of the second node (e.g., a volume on-diskinofile comprising inode information of storage objects maintained bythe second node) is grown on-demand (e.g., when necessary) when an inodenumber beyond a current inofile size is needed to be allocated by areplication operation, such as a create operation. The inofile can begrown by a unit that is a chunk of inodes, such as multiple inodes, inorder to efficiently utilize storage space and avoid frequent pathlength increase operations.

In an embodiment, access control list (ACL) file handle parity isprovided between the first node and the second node to avoid inode maplookups at the second node in order to avoid increased latency incurredby such lookups. The ACL file handle parity corresponds to maintainingparity between inode number and generation number pairings used toreference storage objects (e.g., used as file handles to access storageobjects). Access control lists may be implemented as files in publicinode space. Access control lists specify access control entities (ACEs)as content. An access control list allows an external entity, such as aclient, to specify access control and permissions for storage objectshosted by nodes. An incoming operation will specify access controlentities. The first node attempts to locate an existing access controllist inode with the same access control entities. If an access controllist inode is found, then the access control list inode is used,otherwise, a new access control list inode is created (e.g., a new filehandle is created/allocated). An access control list inode maycorrespond to a file handle for a storage object, which is comprised ofan inode number and generation number. Access control list file handleinformation is replicated from the first node to the second node inorder to achieve parity. If the first node shared or allocated an accesscontrol inode number, then the second node will do the same.

In an embodiment, operations are replicated to the second node when suchoperations result in on-disk modifications. Operations that do notresult in on-disk modifications are not replicated to the second node tosave network bandwidth and CPU cycles of the second node. That is, if anoperation results in an on-disk modification by the first node, then theoperation will be replicated to the second node for execution.Otherwise, the operation will not be replicated. In an example, certainoperations such as open, close, set attribute (e.g., set a delete onclose flag in an in-memory lock), and/or a write with a zero payloadwill not result in an on-disk modification, and thus will not bereplicated.

In an embodiment, punched holes are replicated from the first node tothe second node. That is, the first node may hole punch unused datablocks of the first storage object so that the unused data blocks can bereturned to a storage array for storing other data. While in a steadystate of synchronous replication, it may be easy to merely forward punchhole operations to the first node and the second node for freeing unuseddata blocks back to the storage array. However, issues can occur duringa transition operation where operations are not being replicated in theorder of execution on the first node, and thus a hole punch operationcould attempt to free a block that is beyond an end of the secondstorage object and will fail. Accordingly, when the hole punch operationfails at the second node, then hole punch operation is returned to areplication layer thread at the second node that will issue a write tothe block targeted by the hole punch (e.g., a last block number asspecified by the hole punch) in order to grow the second storage objectso that the hole punch operation can be re-issued. The re-issued holepunch operation will succeed because the second storage object has beengrown to encompass the last block number targeted by the hole punchoperation.

In an embodiment, hole reservations are replicated between the firstnode and the second node. Common internet file system (CIFS)applications may reserve storage space within storage objects beforewriting to the storage objects. Certain operations, such as writes andset attributes, can cause persistent hole reservations being on or offbased on a hole reservation flag. However, details of the holereservation flag can be lost during a transition operation becauseoperations are not replicated in order and the dirty region log does nothave details of the hole reservation flag which can be lost.

During the transition operation, hole reservation flags of operationstargeting the first storage object are replicated within replicationoperations targeting the second storage object so that the holereservation flags are not lost at the second node. In an example, acomponent (e.g., a read handler, a set attribute handler, etc.) willdetect if an inode has a hole reservation flag, and will set a spacereservation attribute that is transmitted to the second node to reservecorresponding storage space within the second storage object. For adirty region log induced read, if a hole reservation flag is set on thefirst object, then the hole reservation flag is set for a write beingsent to the second storage node to reserve corresponding storage spacewithin the second storage object.

During the transition, a source side set attribute operation will detectif the first object has a hole reservation flag. If the first object hasthe hole reservation flag, then the set attribute operation, to bequeued in the metadata log, will contain a flag to turn the holereservations on. When the set attribute operation is replicated andexecuted on the second storage object, the object will also have holereservations turned on.

During the quick reconciliation, read operations to the second node aremodified to convey a presence of hole reservation flags. The resultantWrite and PunchHole operations to the second node are modified to setreservation flags if inodes at the first node had the hole reservationflags. In this way, hole reservation flags are conveyed to the secondnode so that the second node can reserve storage space within the secondstorage object corresponding to reserved storage space within the firststorage object.

In an embodiment, file access permission policy flags (fpolicy flags)are handled without going out of sync (e.g., without transition from asynchronous replication state to an asynchronous replication state). Inan example, when an fpolicy is configured, operations may carry fpolicyflags, which could be failed with a specific error back to an externalfpolicy server for further screening. Once cleared, an operation is sentback to the file system without the fpolicy flag. Because of parallelsplitting of write operations, failure of the write operations willtrigger a quick reconciliation that would take the synchronousreplication relationship out of sync if the reconciliation is not fastenough. Accordingly, write operations having fpolicy flags aresequentially replicated to the second node, as opposed to beingreplicated in parallel. This avoids potential quick reconciliations frombeing triggered. Writes without fpolicy flags will continue to useparallel split for lower latency.

In an embodiment, composite zombie handling is supported. CIFS supportsmultiple data streams for a file/directory, where more than one datastream is associated with a filename (e.g., a name of the first storageobject). When a file system of the first node unlinks/deletes a storageobject which has associated data streams, a base is deleted and theunlink operation completes immediately. The remaining storage objectsare deleted later when a composite zombie handler processes the storageobjects. However, the composite zombie handler at the first node can befast, but is slow at the second node. If an inode number is freed andreused by a create operation at the first node, then the inode numbermay not yet be freed at the second node by a composite zombie handlerprocess hosted by the second node. This will cause the replicationoperation to fail. To avoid the failure, the inode at the second node ishijacked. If the inode is a leaf inode, then the inode is freed up andthe inode number is used immediately for a replicated create operation.If the inode is a stream directory, then the streams are moved under anew private inode and the inode is released.

To provide for the techniques provided herein, FIG. 1 illustrates anembodiment of a clustered network environment 100 or a network storageenvironment. It may be appreciated, however, that the techniques, etc.described herein may be implemented within the clustered networkenvironment 100, a non-cluster network environment, and/or a variety ofother computing environments, such as a desktop computing environment.That is, the instant disclosure, including the scope of the appendedclaims, is not meant to be limited to the examples provided herein. Itwill be appreciated that where the same or similar components, elements,features, items, modules, etc. are illustrated in later figures but werepreviously discussed with regard to prior figures, that a similar (e.g.,redundant) discussion of the same may be omitted when describing thesubsequent figures (e.g., for purposes of simplicity and ease ofunderstanding).

FIG. 1 is a block diagram illustrating the clustered network environment100 that may implement at least some embodiments of the techniquesand/or systems described herein. The clustered network environment 100comprises data storage systems 102 and 104 that are coupled over acluster fabric 106, such as a computing network embodied as a privateInfiniband, Fibre Channel (FC), or Ethernet network facilitatingcommunication between the data storage systems 102 and 104 (and one ormore modules, component, etc. therein, such as, nodes 116 and 118, forexample). It will be appreciated that while two data storage systems 102and 104 and two nodes 116 and 118 are illustrated in FIG. 1, that anysuitable number of such components is contemplated. In an example, nodes116, 118 comprise storage controllers (e.g., node 116 may comprise aprimary or local storage controller and node 118 may comprise asecondary or remote storage controller) that provide client devices,such as host devices 108, 110, with access to data stored within datastorage devices 128, 130. Similarly, unless specifically providedotherwise herein, the same is true for other modules, elements,features, items, etc. referenced herein and/or illustrated in theaccompanying drawings. That is, a particular number of components,modules, elements, features, items, etc. disclosed herein is not meantto be interpreted in a limiting manner.

It will be further appreciated that clustered networks are not limitedto any particular geographic areas and can be clustered locally and/orremotely. Thus, In an embodiment a clustered network can be distributedover a plurality of storage systems and/or nodes located in a pluralityof geographic locations; while In an embodiment a clustered network caninclude data storage systems (e.g., 102, 104) residing in a samegeographic location (e.g., in a single onsite rack of data storagedevices).

In the illustrated example, one or more host devices 108, 110 which maycomprise, for example, client devices, personal computers (PCs),computing devices used for storage (e.g., storage servers), and othercomputers or peripheral devices (e.g., printers), are coupled to therespective data storage systems 102, 104 by storage network connections112, 114. Network connection may comprise a local area network (LAN) orwide area network (WAN), for example, that utilizes Network AttachedStorage (NAS) protocols, such as a Common Internet File System (CIFS)protocol or a Network File System (NFS) protocol to exchange datapackets, a Storage Area Network (SAN) protocol, such as Small ComputerSystem Interface (SCSI) or Fiber Channel Protocol (FCP), an objectprotocol, such as S3, etc. Illustratively, the host devices 108, 110 maybe general-purpose computers running applications, and may interact withthe data storage systems 102, 104 using a client/server model forexchange of information. That is, the host device may request data fromthe data storage system (e.g., data on a storage device managed by anetwork storage control configured to process I/O commands issued by thehost device for the storage device), and the data storage system mayreturn results of the request to the host device via one or more storagenetwork connections 112, 114.

The nodes 116, 118 on clustered data storage systems 102, 104 cancomprise network or host nodes that are interconnected as a cluster toprovide data storage and management services, such as to an enterprisehaving remote locations, cloud storage (e.g., a storage endpoint may bestored within a data cloud), etc., for example. Such a node in theclustered network environment 100 can be a device attached to thenetwork as a connection point, redistribution point or communicationendpoint, for example. A node may be capable of sending, receiving,and/or forwarding information over a network communications channel, andcould comprise any device that meets any or all of these criteria. Oneexample of a node may be a data storage and management server attachedto a network, where the server can comprise a general purpose computeror a computing device particularly configured to operate as a server ina data storage and management system.

In an example, a first cluster of nodes such as the nodes 116, 118(e.g., a first set of storage controllers configured to provide accessto a first storage aggregate comprising a first logical grouping of oneor more storage devices) may be located on a first storage site. Asecond cluster of nodes, not illustrated, may be located at a secondstorage site (e.g., a second set of storage controllers configured toprovide access to a second storage aggregate comprising a second logicalgrouping of one or more storage devices). The first cluster of nodes andthe second cluster of nodes may be configured according to a disasterrecovery configuration where a surviving cluster of nodes providesswitchover access to storage devices of a disaster cluster of nodes inthe event a disaster occurs at a disaster storage site comprising thedisaster cluster of nodes (e.g., the first cluster of nodes providesclient devices with switchover data access to storage devices of thesecond storage aggregate in the event a disaster occurs at the secondstorage site).

As illustrated in the clustered network environment 100, nodes 116, 118can comprise various functional components that coordinate to providedistributed storage architecture for the cluster. For example, the nodescan comprise network modules 120, 122 and disk modules 124, 126. Networkmodules 120, 122 can be configured to allow the nodes 116, 118 (e.g.,network storage controllers) to connect with host devices 108, 110 overthe storage network connections 112, 114, for example, allowing the hostdevices 108, 110 to access data stored in the distributed storagesystem. Further, the network modules 120, 122 can provide connectionswith one or more other components through the cluster fabric 106. Forexample, in FIG. 1, the network module 120 of node 116 can access asecond data storage device by sending a request through the disk module126 of node 118.

Disk modules 124, 126 can be configured to connect one or more datastorage devices 128, 130, such as disks or arrays of disks, flashmemory, or some other form of data storage, to the nodes 116, 118. Thenodes 116, 118 can be interconnected by the cluster fabric 106, forexample, allowing respective nodes in the cluster to access data on datastorage devices 128, 130 connected to different nodes in the cluster.Often, disk modules 124, 126 communicate with the data storage devices128, 130 according to the SAN protocol, such as SCSI or FCP, forexample. Thus, as seen from an operating system on nodes 116, 118, thedata storage devices 128, 130 can appear as locally attached to theoperating system. In this manner, different nodes 116, 118, etc. mayaccess data blocks through the operating system, rather than expresslyrequesting abstract files.

It should be appreciated that, while the clustered network environment100 illustrates an equal number of network and disk modules, otherembodiments may comprise a differing number of these modules. Forexample, there may be a plurality of network and disk modulesinterconnected in a cluster that does not have a one-to-onecorrespondence between the network and disk modules. That is, differentnodes can have a different number of network and disk modules, and thesame node can have a different number of network modules than diskmodules.

Further, a host device 108, 110 can be networked with the nodes 116, 118in the cluster, over the storage networking connections 112, 114. As anexample, respective host devices 108, 110 that are networked to acluster may request services (e.g., exchanging of information in theform of data packets) of nodes 116, 118 in the cluster, and the nodes116, 118 can return results of the requested services to the hostdevices 108, 110. In an embodiment, the host devices 108, 110 canexchange information with the network modules 120, 122 residing in thenodes 116, 118 (e.g., network hosts) in the data storage systems 102,104.

In an embodiment, the data storage devices 128, 130 comprise volumes132, which is an implementation of storage of information onto diskdrives or disk arrays or other storage (e.g., flash) as a file-systemfor data, for example. In an example, a disk array can include alltraditional hard drives, all flash drives, or a combination oftraditional hard drives and flash drives. Volumes can span a portion ofa disk, a collection of disks, or portions of disks, for example, andtypically define an overall logical arrangement of file storage on diskspace in the storage system. In an embodiment a volume can comprisestored data as one or more files that reside in a hierarchical directorystructure within the volume.

Volumes are typically configured in formats that may be associated withparticular storage systems, and respective volume formats typicallycomprise features that provide functionality to the volumes, such asproviding an ability for volumes to form clusters. For example, where afirst storage system may utilize a first format for their volumes, asecond storage system may utilize a second format for their volumes.

In the clustered network environment 100, the host devices 108, 110 canutilize the data storage systems 102, 104 to store and retrieve datafrom the volumes 132. In this embodiment, for example, the host device108 can send data packets to the network module 120 in the node 116within data storage system 102. The node 116 can forward the data to thedata storage device 128 using the disk module 124, where the datastorage device 128 comprises volume 132A. In this way, in this example,the host device can access the volume 132A, to store and/or retrievedata, using the data storage system 102 connected by the storage networkconnection 112. Further, in this embodiment, the host device 110 canexchange data with the network module 122 in the node 118 within thedata storage system 104 (e.g., which may be remote from the data storagesystem 102). The node 118 can forward the data to the data storagedevice 130 using the disk module 126, thereby accessing volume 1328associated with the data storage device 130.

It may be appreciated that techniques provided herein may be implementedwithin the clustered network environment 100. It may be appreciated thattechniques provided herein may be implemented for and/or between anytype of computing environment, and may be transferable between physicaldevices (e.g., node 116, node 118, a desktop computer, a tablet, alaptop, a wearable device, a mobile device, a storage device, a server,etc.) and/or a cloud computing environment (e.g., remote to theclustered network environment 100).

FIG. 2 is an illustrative example of a data storage system 200 (e.g.,102, 104 in FIG. 1), providing further detail of an embodiment ofcomponents that may implement one or more of the techniques and/orsystems described herein. The data storage system 200 comprises a node202 (e.g., nodes 116, 118 in FIG. 1), and a data storage device 234(e.g., data storage devices 128, 130 in FIG. 1). The node 202 may be ageneral purpose computer, for example, or some other computing deviceparticularly configured to operate as a storage server. A host device205 (e.g., 108, 110 in FIG. 1) can be connected to the node 202 over anetwork 216, for example, to provide access to files and/or other datastored on the data storage device 234. In an example, the node 202comprises a storage controller that provides client devices, such as thehost device 205, with access to data stored within data storage device234.

The data storage device 234 can comprise mass storage devices, such asdisks 224, 226, 228 of a disk array 218, 220, 222. It will beappreciated that the techniques and systems, described herein, are notlimited by the example embodiment. For example, disks 224, 226, 228 maycomprise any type of mass storage devices, including but not limited tomagnetic disk drives, flash memory, and any other similar media adaptedto store information, including, for example, data (D) and/or parity (P)information.

The node 202 comprises one or more processors 204, a memory 206, anetwork adapter 210, a cluster access adapter 212, and a storage adapter214 interconnected by a system bus 242. The data storage system 200 alsoincludes an operating system 208 installed in the memory 206 of the node202 that can, for example, implement a Redundant Array of Independent(or Inexpensive) Disks (RAID) optimization technique to optimize areconstruction process of data of a failed disk in an array.

The operating system 208 can also manage communications for the datastorage system, and communications between other data storage systemsthat may be in a clustered network, such as attached to a cluster fabric215 (e.g., 106 in FIG. 1). Thus, the node 202, such as a network storagecontroller, can respond to host device requests to manage data on thedata storage device 234 (e.g., or additional clustered devices) inaccordance with these host device requests. The operating system 208 canoften establish one or more file systems on the data storage system 200,where a file system can include software code and data structures thatimplement a persistent hierarchical namespace of files and directories,for example. As an example, when a new data storage device (not shown)is added to a clustered network system, the operating system 208 isinformed where, in an existing directory tree, new files associated withthe new data storage device are to be stored. This is often referred toas “mounting” a file system.

In the example data storage system 200, memory 206 can include storagelocations that are addressable by the processors 204 and adapters 210,212, 214 for storing related software application code and datastructures. The processors 204 and adapters 210, 212, 214 may, forexample, include processing elements and/or logic circuitry configuredto execute the software code and manipulate the data structures. Theoperating system 208, portions of which are typically resident in thememory 206 and executed by the processing elements, functionallyorganizes the storage system by, among other things, invoking storageoperations in support of a file service implemented by the storagesystem. It will be apparent to those skilled in the art that otherprocessing and memory mechanisms, including various computer readablemedia, may be used for storing and/or executing application instructionspertaining to the techniques described herein. For example, theoperating system can also utilize one or more control files (not shown)to aid in the provisioning of virtual machines.

The network adapter 210 includes the mechanical, electrical andsignaling circuitry needed to connect the data storage system 200 to ahost device 205 over a network 216, which may comprise, among otherthings, a point-to-point connection or a shared medium, such as a localarea network. The host device 205 (e.g., 108, 110 of FIG. 1) may be ageneral-purpose computer configured to execute applications. Asdescribed above, the host device 205 may interact with the data storagesystem 200 in accordance with a client/host model of informationdelivery.

The storage adapter 214 cooperates with the operating system 208executing on the node 202 to access information requested by the hostdevice 205 (e.g., access data on a storage device managed by a networkstorage controller). The information may be stored on any type ofattached array of writeable media such as magnetic disk drives, flashmemory, and/or any other similar media adapted to store information. Inthe example data storage system 200, the information can be stored indata blocks on the disks 224, 226, 228. The storage adapter 214 caninclude input/output (I/O) interface circuitry that couples to the disksover an I/O interconnect arrangement, such as a storage area network(SAN) protocol (e.g., Small Computer System Interface (SCSI), iSCSI,hyperSCSI, Fiber Channel Protocol (FCP)). The information is retrievedby the storage adapter 214 and, if necessary, processed by the one ormore processors 204 (or the storage adapter 214 itself) prior to beingforwarded over the system bus 242 to the network adapter 210 (and/or thecluster access adapter 212 if sending to another node in the cluster)where the information is formatted into a data packet and returned tothe host device 205 over the network 216 (and/or returned to anothernode attached to the cluster over the cluster fabric 215).

In an embodiment, storage of information on disk arrays 218, 220, 222can be implemented as one or more storage volumes 230, 232 that arecomprised of a cluster of disks 224, 226, 228 defining an overalllogical arrangement of disk space. The disks 224, 226, 228 that compriseone or more volumes are typically organized as one or more groups ofRAIDs. As an example, volume 230 comprises an aggregate of disk arrays218 and 220, which comprise the cluster of disks 224 and 226.

In an embodiment, to facilitate access to disks 224, 226, 228, theoperating system 208 may implement a file system (e.g., write anywherefile system) that logically organizes the information as a hierarchicalstructure of directories and files on the disks. In this embodiment,respective files may be implemented as a set of disk blocks configuredto store information, whereas directories may be implemented asspecially formatted files in which information about other files anddirectories are stored.

Whatever the underlying physical configuration within this data storagesystem 200, data can be stored as files within physical and/or virtualvolumes, which can be associated with respective volume identifiers,such as file system identifiers (FSIDs), which can be 32-bits in lengthin one example.

A physical volume corresponds to at least a portion of physical storagedevices whose address, addressable space, location, etc. doesn't change,such as at least some of one or more data storage devices 234 (e.g., aRedundant Array of Independent (or Inexpensive) Disks (RAID system)).Typically the location of the physical volume doesn't change in that the(range of) address(es) used to access it generally remains constant.

A virtual volume, in contrast, is stored over an aggregate of disparateportions of different physical storage devices. The virtual volume maybe a collection of different available portions of different physicalstorage device locations, such as some available space from each of thedisks 224, 226, and/or 228. It will be appreciated that since a virtualvolume is not “tied” to any one particular storage device, a virtualvolume can be said to include a layer of abstraction or virtualization,which allows it to be resized and/or flexible in some regards.

Further, a virtual volume can include one or more logical unit numbers(LUNs) 238, directories 236, Qtrees 235, and files 240. Among otherthings, these features, but more particularly LUNS, allow the disparatememory locations within which data is stored to be identified, forexample, and grouped as data storage unit. As such, the LUNs 238 may becharacterized as constituting a virtual disk or drive upon which datawithin the virtual volume is stored within the aggregate. For example,LUNs are often referred to as virtual drives, such that they emulate ahard drive from a general purpose computer, while they actually comprisedata blocks stored in various parts of a volume.

In an embodiment, one or more data storage devices 234 can have one ormore physical ports, wherein each physical port can be assigned a targetaddress (e.g., SCSI target address). To represent respective volumesstored on a data storage device, a target address on the data storagedevice can be used to identify one or more LUNs 238. Thus, for example,when the node 202 connects to a volume 230, 232 through the storageadapter 214, a connection between the node 202 and the one or more LUNs238 underlying the volume is created.

In an embodiment, respective target addresses can identify multipleLUNs, such that a target address can represent multiple volumes. The I/Ointerface, which can be implemented as circuitry and/or software in thestorage adapter 214 or as executable code residing in memory 206 andexecuted by the processors 204, for example, can connect to volume 230by using one or more addresses that identify the one or more LUNs 238.

It may be appreciated that techniques provided herein may be implementedfor the data storage system 200. It may be appreciated that techniquesprovided herein may be implemented for and/or between any type ofcomputing environment, and may be transferable between physical devices(e.g., node 202, host device 205, a desktop computer, a tablet, alaptop, a wearable device, a mobile device, a storage device, a server,etc.) and/or a cloud computing environment (e.g., remote to the node 202and/or the host device 205).

One embodiment of timestamp consistency is illustrated by an exemplarymethod 300 of FIG. 3 and further described in conjunction with system400 of FIGS. 4A-4C. A first node 402 (e.g., a storage controller, astorage server, a computing device, a storage service, or any otherhardware or software capable of storing data) may store a first storageobject 404 (e.g., a file, a LUN, a storage virtual machine, a volume, aconsistency group, a directory, or any other set of data), asillustrated by FIG. 4A. The first storage object 404 may have asynchronous replication relationship with a second storage object 412stored by a second node 410. The second storage object 412 may bemaintained as a replica of the first storage object 404. A splittercomponent is configured to replicate operations targeting the firststorage object 404 to the second storage object 412. In particular, thesplitter component is configured to intercept operations before suchoperations reach a file system or operating system of the first node402. The splitter component is configured to split (replicate) anoperation to create a replication operation that is transmitted to thesecond node 410 for execution upon the second storage object 412. Theoperation is only acknowledged back to a device that sent the operationto the first node 402 once execution and replication of the operationare acknowledged.

Timestamps (e.g., a modify timestamp, a create timestamp) are usuallyassigned to storage objects and/or update by the nodes based upon whenoperations and replication operations are executed upon the storageobjects. Replicating the timestamp information to the second node 410 ina consistent matter is useful because the timestamp information can beused by the second node 410 to perform data integrity validation,incremental backups, etc. Generally, a timestamp is assigned using a gettime of day function when an operation (e.g., a write operation, acreate operation, etc.) is executed in order to set an mtime and/orctime of storage objects modified by the operation. However, withparallel splitting the second node 410 will not know what time the firstnode 402 used. This results in timestamp inconsistency between the firststorage object 404 and the second storage object 412.

Accordingly, as provided herein, the splitter component assigns 408 asame timestamp to both the operation and the replication operation sothat the same timestamp value is used by both the first node 402 and thesecond node 410. For example, the first node 402 receives an operation406 from a device, such as a write operation that is to modify the firststorage object 404, at 302. At 304, the splitter component assigns atimestamp to the operation. At 306, the splitter component creates areplication operation 414 that is a replication of the operation 406. At308, the splitter component assigns 408 the same timestamp to thereplication operation 414 that the splitter component assigned to theoperation 406.

At 310, the operation 406 is implemented upon the first storage object404 by the first node 402 and the replication operation 414 isreplicated to the second node 410 for implementation upon the secondstorage object 412. A file system operation handler of the first node402 is reconfigured to use the timestamp assigned to the operation 406by the splitter component instead of creating and using a new timestampcorresponding to a time that the operation 406 is executed by the firstnode 402. A file system operation handler of the second node 410 isreconfigured to use the timestamp assigned to the replication operation414 by the splitter component instead of creating and using a newtimestamp corresponding to a time that the replication operation 414 isexecuted by the second node 410.

If the timestamp assigned to the replication operation 414 is largerthan a current timestamp of the second storage object 412, then thetimestamp is assigned as a new current timestamp for the second storageobject 412 (otherwise the timestamp is not assigned). If the timestampassigned to the operation 406 is larger than a current timestamp of thefirst storage object 404, then the timestamp from the operation 406 isassigned as a new current timestamp for the first storage object 404(otherwise the timestamp is not assigned).

FIG. 4B illustrates the first node 402 selectively replicating 422certain operations 420 to the second node 410 for execution. In anembodiment, operations are replicated from the first node 402 to thesecond node 410 when such operations result in on-disk modifications.Otherwise, operations that do not results in on-disk modifications arenot replicated to the second node 410 and are merely locally executed atthe first node 402 to save network bandwidth and CPU cycles of thesecond node 410. That is, if an operation results in an on-diskmodification by the first node 402 (e.g., naming an object, deleting anobject, write data or metadata to storage, creating a new object, or anyother operation that results in creating or modifying data withinstorage), then the operation will be replicated to the second node 410for execution. Otherwise, the operation will not be replicated. In anexample, certain operations such as an open operation (e.g., opening afile), a close operation (e.g., closing the file), a set attributeoperation (e.g., set a delete on close flag in an in-memory lock),and/or a write with a zero payload will not result in an on-diskmodification, and thus will not be replicated.

FIG. 4C illustrates the first node 402 and the second node 410sequentially replicating operations having file access permission policyflags (fpolicy flags). In an example, an fpolicy is configured by aclient that stores data within a storage environment comprising thefirst node 402 and the second node 410. The fpolicy allows externalclient applications to connect to the storage environment in order tomonitor and set file access permissions. The file access permissions maycorrespond to how to handle create operations, open operations, renameoperations, delete operations, along with permission for certain typesof files and whether a client application (e.g., an fpolicy server thatscreens operations with fpolicy flags) is to be notified of a remotedevice attempting to execute an operation to access a storage object.When an operation with the fpolicy flag is received by a file system,the operation may be failed back to the fpolicy server for screening tosee whether the operation is allowed (e.g., the file system failsoperations back to the fpolicy server if the operations have the fpolicyflag). Upon the remote device being cleared by the fpolicy server foraccessing the storage object, the operation is sent without the fpolicyflag to the file system for execution. The operation does not have thefpolicy flag so that the file system will not fail the operation.

Because of parallel splitting of write operations, failure of the writeoperations will trigger a quick reconciliation that would take thesynchronous replication relationship between the first node 402 and thesecond node 410 (e.g., between the first storage object 404 and thesecond storage object 412) out of sync if the quick reconciliation failsto complete the operation (Op) quickly (e.g., within a thresholdtimespan). Accordingly, fpolicy flags are handled without going out ofsync (e.g., without transition from a synchronous replication state toan asynchronous replication state). In particular, write operations 430with fpolicy flags are sequentially replicated 434 to the second node410, as opposed to being replicated in parallel. For example, anoperation is replicated to the second node 410 for execution upon thesecond storage object 412 as a replication operation only after thefirst node 402 has successfully executed the operation upon the firststorage object 404. This avoids potential quick reconciliations frombeing triggered. Write operations 432 without fpolicy flags will bereplicated 436 in parallel for lower latency (e.g., replicated to thesecond node 410 regardless of whether the write operations 432 havefinished executing upon the first storage object 404).

One embodiment of inofile management is illustrated by an exemplarymethod 500 of FIG. 5 and further described in conjunction with system600 of FIGS. 6A-6C. A first node 602 may store a first storage object604, as illustrated by FIG. 6A. The first storage object 604 may have areplication relationship with a second storage object 612 stored by asecond node 610. The second storage object 612 may be maintained as areplica of the first storage object 604. A splitter component isconfigured to replicate operations targeting the first storage object604 to the second storage object 612. While in a synchronous replicationstate, the splitter component is configured to intercept operationsbefore such operations reach a file system or operating system of thefirst node 602. The splitter component is configured to split(replicate) an operation to create a replication operation that istransmitted to the second node 610 for execution upon the second storageobject 612. The operation is acknowledged back to a device that sent theoperation to the first node 602 once execution and replication of theoperation are acknowledged.

The first node 602 may maintain an inofile, such as a volume on-diskinofile comprising inode information of storage objects maintained bythe first node 602. The second node 610 may maintain an inofile 614,such as a volume on-disk inofile comprising inode information of storageobjects maintained by the second node 610. As provided herein, theinofile 614 of the second node 610 is grown on-demand when necessary. Inparticular, the inofile 614 is grown when an inode number beyond acurrent inofile size of the inofile 614 is needed to be allocated by areplication operation, such as a create operation being replicated tothe second node 610.

In particular, when metadata operations, such as a create operation, isreplicated from the first node 602 to the second node 610, the operationwill have an inode number and generation number as an identifier of theoperation. The identifier is replicated along with the operation to thesecond node 610. If the inode number is greater than the current inofilesize of the inofile 614 (e.g., new data is being created within thesecond storage object 612 or a new storage object is being created withthe new data), then the second node 610 determines that the inode numberof the replicated identifier is not found within the inofile 614 becausethe inode number is beyond the current inofile size of the inofile 614.Accordingly, the second node 610 sends the replication operation back tothe first node 602 so that an inofile grow operation can be issued toincrease the size of the inofile 614 on-demand to accommodate thereplication operation (e.g., as opposed to initially preallocating theinofile 614 to a large size that remains used until needed, which canwaste storage space). The inofile 614 can be grown by a unit that is achunk of inodes, such as multiple inodes, in order to efficientlyutilize storage space and avoid frequent path length increaseoperations.

In an embodiment, the first node 602 receives an operation 606, such asa create operation, at 502. The operation 606 has an identifierspecifying an inode number and generation number of data to be createdby the create operation. The inode number may correspond to an inodebeing allocated by the create operation. The operation 606 is replicatedas a replication operation 616 comprising a replicated identifierspecifying the inode number and generation number, at 504. The firstnode 602 locally executes the operation 606 and the replicationoperation 616 is transmitted to the second node 610, at 506.

The second node 610 compares 608 the inode number being allocated to thecurrent size of inofile 614. If the inode number is greater than thecurrent size of the inofile 614, then the second node 610 may return thereplication operation 616 back to the first node 602 with an indicationthat a size of the inofile 614 needs to be increased, as illustrated byFIG. 6A. At 508, the current size of the inofile 614 is grown 618 byeither a single inode or by multiple inodes (a chunk of inodes). Thereplication operation 616 is then executed by the second node 610 basedupon the inofile 614 being grown 618. In contrast, if the inode numberis less than or equal to the current size of the inofile 614, then theinofile is not grown and the replication operation 616 is executed bythe second node 610, as illustrated by FIG. 6B. In this way, the inofile614 is grown on-demand only as needed.

FIG. 6C illustrates access control list (ACL) file handle parity 624being implemented for the first node 602 and the second node 610 toavoid inode map lookups at the second node 610, which would otherwiseincrease latency due to such lookups. The ACL file handle parity 624corresponds to maintaining parity between inode number and generationnumber pairings used to reference storage objects (e.g., used as filehandles to access storage objects). Access control lists may beimplemented as files in a public inode space. Access control listsspecify access control entities (ACEs) as content. An access controllist allows an external entity, such as a client, to specify accesscontrol and permissions for storage objects hosted by nodes.

An incoming operation will specify access control entities. The accesscontrol entities are used by the first node 602 to attempt to locate anaccess control list inode with the same access control entities. If anaccess control list inode is found that has the same access controlentities specified by the incoming operation, then the access controllist inode is shared and referenced by the incoming operation.Otherwise, if there is no access control list inode with the same accesscontrol entities, a new access control list inode is created/allocatedfor the incoming operation (e.g., a new file handle iscreated/allocated). Access control list sharing is a best effort by thefirst node 602 based upon what access control lists are in memory. Inthis way, the first node 602 will either share the existing accesscontrol list inode or create/allocate a new access control list inode.As provided herein, the second node 610 will be controlled to mimic whatthe first node 602 did, such as either share or allocate.

An access control list inode may correspond to a file handle for astorage object, which is comprised of an inode number and generationnumber. Access control list file handle information is replicated fromthe first node 602 to the second node 610 in order to achieve parity.Thus, if the first node 602 shared or allocated an access control listinode, then the second node 610 will do the same. For example, when anoperation is replicated to the second node 610 as a replicationoperation, the replication operation may specify details of whether anaccess control list inode number was allocated or shared by the firstnode 602. Accordingly, a file system operation handler of the secondnode 610 will bypass default logic of access control list inode numbersharing and instead mimic whatever the first node 602 did, such asallocating a new access control list inode (e.g., creating a new accesscontrol list inode as a new file handle) or sharing an existing accesscontrol list inode of an access control list having the same accesscontrol entities of the replication operation. In this way, accesscontrol list file handle party 624 is maintained between inode numberand generation number pairings 620 maintained by the first node 602 andinode number and generation number pairings 622 maintained by the secondnode 610 because the second node 610 will either share an existingaccess control list inode or allocate a new access control list inodebased upon whether the first node 602 shared or allocated.

One embodiment of freeing and utilizing unused inodes is illustrated byan exemplary method 700 of FIG. 7 and further described in conjunctionwith system 800 of FIG. 8. A first node 802 may store a first storageobject 804, as illustrated by FIG. 8. The first storage object 804 mayhave a replication relationship with a second storage object 808 storedby a second node 806. The second storage object 808 may be maintained asa replica of the first storage object 804. A splitter component isconfigured to replicate operations targeting the first storage object604 to the second storage object 612. While in a synchronous replicationstate, the splitter component is configured to intercept operationsbefore such operations reach a file system or operating system of thefirst node 802. The splitter component is configured to split(replicate) an operation to create a replication operation that istransmitted to the second node 806 for execution upon the second storageobject 808. The operation is acknowledged back to a device that sent theoperation to the first node 802 once execution and replication of theoperation are acknowledged.

A storage environment, comprising the first node 802 and the second node806, may support alternate data streams. This allows multiple datastreams to be associated with a name of the first storage object 804and/or multiple data streams to be associated with a name of the secondstorage object 808. A stream name of a data stream identifies a dataattribute of a corresponding storage object.

In an embodiment, composite zombie handling is supported for replicatingoperations from the first node 802 to the second node 806. Compositezombie handling corresponds to freeing and utilizing unused inodes atthe second node 806 (e.g., inodes of data no longer used or referencedby storage objects of the second node 806) that have yet to be freed bya composite zombie handler of the second node 806. CIFS supportsmultiple data streams for a file/directory, where more than one datastream is associated with a filename (e.g., a name of the first storageobject). When a file system of the first node 802 unlinks a storageobject associated with data streams, a base is deleted and the unlinkoperation completes immediately. The remaining storage objects aredeleted later when a composite zombie handler processes the storageobjects. However, the composite zombie handler at the first node 802 canbe fast, but a composite zombie handler at the second node 806 can bemuch slower. Thus, if an inode number is freed and reused by a createoperation at the first node 802, then the inode number may not yet befreed at the second node 806 by the composite zombie handler hosted bythe second node 806. This will cause a replication operation of thecreate operation to fail. To avoid the failure, the inode at the secondnode 806 is hijacked. If the inode is a leaf inode, then the inode isfreed up and used immediately for the replicated create operation. Ifthe inode is a stream directory, then the data streams are moved under anew private inode and the inode is released.

In an embodiment, an operation 812, targeting the first storage object804 of the first node 802, in intercepted, at 702. At 704, a replicationoperation 816 is created as a replication of the operation 812. At 706,the operation 812 is implemented upon the first storage object 804 bythe first node 802. An inode number may be freed and reused by the firstnode 802 for processing the operation 812. The replication operation 816may be transmitted to the second node 806 for execution. At 708, adetermination is made as to whether the replication operation uses aninode 810 no longer used by storage objects of the second node 806. Thedetermination may include determining that the composite zombie handlerof the second node 806 has yet to free the inode 810. The determinationmay include determining that the replication operation 816 comprises anoperation, such as a create operation, targeting the inode 810.

The inode 810 is evaluated 814 to see if the inode 810 is a leaf inodeor a stream directory inode not in use. If the inode is a leaf inode,then the inode 810 is freed and utilized for the replication operation816, at 710, even though the composite zombie handler of the second node806 has not yet freed the inode 810. If the inode is a stream directoryinode, then data streams of the stream directory inode are moved under anew private inode for use by the replication operation 816, and thestream directory inode is released/freed.

One embodiment of freeing and utilizing unused inodes is illustrated byan exemplary method 900 of FIG. 9 and further described in conjunctionwith system 1000 of FIGS. 10A and 10B. A first node 1002 may store afirst storage object 1004, as illustrated by FIG. 10A. The first storageobject 1004 may have a replication relationship with a second storageobject 1008 stored by a second node 1006. The second storage object 1008may be maintained as a replica of the first storage object 1004. Asplitter component is configured to replicate operations targeting thefirst storage object 1004 to the second storage object 1008. While in asynchronous replication state, the splitter component is configured tointercept operations before such operations reach a file system oroperating system of the first node 1002. The splitter component isconfigured to split (replicate) an operation to create a replicationoperation that is transmitted to the second node 1006 for execution uponthe second storage object 1008. The operation is acknowledged back to adevice that sent the operation to the first node 1002 once execution andreplication of the operation are acknowledged.

If the first storage object 1004 and the second storage object 1008 fallout of sync such that incoming operations are not synchronouslyreplicated to the second storage object 1008, a transition operation canbe performed to provide non-disruptive re-synchronization between thefirst node 1002 and the second node 1006. The transition operation canbe performed using a dirty region log 1010 to track dirty regions of thefirst storage object 1004 modified during the transition operation and ametadata log to track metadata operations executed during the transitionoperation. Dirty data (e.g., modified data of the first storage object1004 not yet replicated to the second storage object 1008) as identifiedby the dirty region log 1010 and metadata operations as logged by themetadata log are applied to the second node 1006 to bring the firststorage object 1004 and the second storage object 1008 into asynchronous replication relationship. Metadata operations are firstreplicated from the metadata log, and then the dirty data is replicated.

If a replication operation succeeded at the second node 1006 but acorresponding operation fails at the first node 1002, then a quickreconciliation (quick reconcile) can be performed. The quickreconciliation will undo the replication operation at the second node1006 using old data from the first node 1002 before responding with afailure. In this way, the first storage object 1004 and the secondstorage object 1008 will be consistent in that they both will comprisethe same old data. A failure message is returned to a client device thatissued the operation because the operation and the replication operationwere not fully executed and committed to write the new data to the firststorage object 1004 and the second storage object 1008. In this way, thesynchronous replication relationship can stay in-sync and the firststorage object 1004 and the second storage object 1008 are consistent.

In an embodiment, persistent hole reservations are replicated betweenthe first node 1002 and the second node 1006. Common internet filesystem (CIFS) applications may reserve storage space within storageobjects before writing to the storage objects. Certain operations, suchas writes and set attributes, can cause persistent hole reservationsbeing on or off based on a hole reservation flag. However, details ofthe hole reservation flag can be lost during the transition operationbecause operations are not replicated in order and the dirty region logdoesn't have details of the hole reservation flag which can be lost.

At 902, the transition operation is performed to provide non-disruptivere-synchronization between the first node 1002 and the second node 1006.The dirty region log 1010 is used to track dirty regions of the firststorage object 1004 modified during the transition operation. A metadatalog is used to track metadata operations executed by the first node1002. During the transition operation, the metadata operations arereplicated to the second node 1006. The dirty regions are thenreplicated to the second storage object 1008. For example, a dirtyregion read is performed to replicate data of a dirty region to thesecond storage object 1008. The dirty region log scan induced readevaluates an inode associated with the dirty region to determine whethera hole reservation flag is set. The data of the dirty region and thehole reservation flag are replicated to the second storage object 1008based upon the hole reservation flag being set.

At 904, the first storage object 1004 and the second storage object 1008are synchronized (e.g., replication of logged metadata operations, andthen replication of dirty data). During the transition operation, holereservation flags of operations targeting the first storage object 1004are replicated 1012 within replication operations targeting the secondstorage object 1008 so that the hole reservation flags are not lost atthe second node 1006, at 906. In an example, a component (e.g., a readhandler, a set attribute handler, etc.) will detect if an inode has ahole reservation flag, and will set a space reservation attribute thatis transmitted to the second node 1006 to reserve corresponding storagespace within the second storage object 1008. For a dirty region loginduced read, if a hole reservation flag is set, then the holereservation flag is set for a write operation being sent to the secondnode 1006 to reserve corresponding storage space within the secondstorage object 1008.

When an operation fails to execute upon the first storage object 1004but a corresponding replication operation succeeds at the second storageobject 1008, the quick reconciliation is performed. During the quickreconciliation, read operations to the second node 1006 are modified toconvey a presence of hole reservation flags. The quick reconciliation(QR) induced operations of Write and PunchHole to the second node 1006will have hole reservation flags if inodes at the first node 1002 hadthe hole reservation flags. In this way, hole reservation flags areconveyed/replicated 1012 to the second node 1006 notwithstanding thequick reconciliation so that the second node 1006 can reserve storagespace within the second storage object 1008 corresponding to reservedstorage space within the first storage object 1004.

FIG. 10B illustrates failure handling 1020 for punch hole operations.During a steady state of synchronous replication, punched holes areforwarded from the first node 1002 to the second node 1006. That is, thefirst node 1002 may hole punch unused data blocks of the first storageobject 1004 so that the unused data blocks can be returned to a storagearray for storing other data. While in the steady state of synchronousreplication, it may be easy to merely forward punch hole operations tothe first node 1002 and the second node 1006 for freeing unused datablocks back to the storage array. However, issues can occur during thetransition operation where operations are not being sequentiallyreplicated, and thus a hole punch operation could attempt to free ablock that is beyond an end of the second storage object 1008 and willfail. Accordingly, when the hole punch operation fails at the secondnode 1006, then the hole punch operation is returned to a replicationlayer thread at the second node 1006 that will issue a write 1022 to theblock targeted by the hole punch operation (e.g., a last block number asspecified by the hole punch operation) in order to grow the secondstorage object 1008 so that the hole punch operation can be re-issued.The re-issued hole punch operation will succeed because the secondstorage object 1008 has been grown to encompass the last block numbertargeted by the hole punch operation.

Still another embodiment involves a computer-readable medium 1100comprising processor-executable instructions configured to implement oneor more of the techniques presented herein. An example embodiment of acomputer-readable medium or a computer-readable device that is devisedin these ways is illustrated in FIG. 11, wherein the implementationcomprises a computer-readable medium 1108, such as a compactdisc-recordable (CD-R), a digital versatile disc-recordable (DVD-R),flash drive, a platter of a hard disk drive, etc., on which is encodedcomputer-readable data 1106. This computer-readable data 1106, such asbinary data comprising at least one of a zero or a one, in turncomprises a processor-executable computer instructions 1104 configuredto operate according to one or more of the principles set forth herein.In some embodiments, the processor-executable computer instructions 1104are configured to perform a method 1102, such as at least some of theexemplary method 300 of FIG. 3, at least some of the exemplary method500 of FIG. 5, at least some of the exemplary method 700 of FIG. 7,and/or at least some of the exemplary method 900 of FIG. 9, for example.In some embodiments, the processor-executable computer instructions 1104are configured to implement a system, such as at least some of theexemplary system 400, at least some of the exemplary system 600, atleast some of the exemplary system 800, and/or at least some of theexemplary system 1000, for example. Many such computer-readable mediaare contemplated to operate in accordance with the techniques presentedherein.

FIG. 12 is a diagram illustrating an example operating environment 1200in which an embodiment of the techniques described herein may beimplemented. In one example, the techniques described herein may beimplemented within a client device 1228, such as a laptop, tablet,personal computer, mobile device, wearable device, etc. In anotherexample, the techniques described herein may be implemented within astorage controller 1230, such as a node configured to manage the storageand access to data on behalf of the client device 1228 and/or otherclient devices. In another example, the techniques described herein maybe implemented within a distributed computing platform 1202 such as acloud computing environment (e.g., a cloud storage environment, amulti-tenant platform, etc.) configured to manage the storage and accessto data on behalf of the client device 1228 and/or other client devices.

In yet another example, at least some of the techniques described hereinare implemented across one or more of the client device 1228, thestorage controller 1230, and the distributed computing platform 1202.For example, the client device 1228 may transmit operations, such asdata operations to read data and write data and metadata operations(e.g., a create file operation, a rename directory operation, a resizeoperation, a set attribute operation, etc.), over a network 1226 to thestorage controller 1230 for implementation by the storage controller1230 upon storage. The storage controller 1230 may store data associatedwith the operations within volumes or other data objects/structureshosted within locally attached storage, remote storage hosted by othercomputing devices accessible over the network 1226, storage provided bythe distributed computing platform 1202, etc. The storage controller1230 may replicate the data and/or the operations to other computingdevices so that one or more replicas, such as a destination storagevolume that is maintained as a replica of a source storage volume, aremaintained. Such replicas can be used for disaster recovery andfailover.

The storage controller 1230 may store the data or a portion thereofwithin storage hosted by the distributed computing platform 1202 bytransmitting the data to the distributed computing platform 1202. In oneexample, the storage controller 1230 may locally store frequentlyaccessed data within locally attached storage. Less frequently accesseddata may be transmitted to the distributed computing platform 1202 forstorage within a data storage tier 1208. The data storage tier 1208 maystore data within a service data store 1220, and may store clientspecific data within client data stores assigned to such clients such asa client (1) data store 1222 used to store data of a client (1) and aclient (N) data store 1224 used to store data of a client (N). The datastores may be physical storage devices or may be defined as logicalstorage, such as a virtual volume, LUNs, or other logical organizationsof data that can be defined across one or more physical storage devices.In another example, the storage controller 1230 transmits and stores allclient data to the distributed computing platform 1202. In yet anotherexample, the client device 1228 transmits and stores the data directlyto the distributed computing platform 1202 without the use of thestorage controller 1230.

The management of storage and access to data can be performed by one ormore storage virtual machines (SVMs) or other storage applications thatprovide software as a service (SaaS) such as storage software services.In one example, an SVM may be hosted within the client device 1228,within the storage controller 1230, or within the distributed computingplatform 1202 such as by the application server tier 1206. In anotherexample, one or more SVMs may be hosted across one or more of the clientdevice 1228, the storage controller 1230, and the distributed computingplatform 1202.

In one example of the distributed computing platform 1202, one or moreSVMs may be hosted by the application server tier 1206. For example, aserver (1) 1216 is configured to host SVMs used to execute applicationssuch as storage applications that manage the storage of data of theclient (1) within the client (1) data store 1222. Thus, an SVM executingon the server (1) 1216 may receive data and/or operations from theclient device 1228 and/or the storage controller 1230 over the network1226. The SVM executes a storage application to process the operationsand/or store the data within the client (1) data store 1222. The SVM maytransmit a response back to the client device 1228 and/or the storagecontroller 1230 over the network 1226, such as a success message or anerror message. In this way, the application server tier 1206 may hostSVMs, services, and/or other storage applications using the server (1)1216, the server (N) 1218, etc.

A user interface tier 1204 of the distributed computing platform 1202may provide the client device 1228 and/or the storage controller 1230with access to user interfaces associated with the storage and access ofdata and/or other services provided by the distributed computingplatform 1202. In an example, a service user interface 1210 may beaccessible from the distributed computing platform 1202 for accessingservices subscribed to by clients and/or storage controllers, such asdata replication services, application hosting services, data securityservices, human resource services, warehouse tracking services,accounting services, etc. For example, client user interfaces may beprovided to corresponding clients, such as a client (1) user interface1212, a client (N) user interface 1214, etc. The client (1) can accessvarious services and resources subscribed to by the client (1) throughthe client (1) user interface 1212, such as access to a web service, adevelopment environment, a human resource application, a warehousetracking application, and/or other services and resources provided bythe application server tier 1206, which may use data stored within thedata storage tier 1208.

The client device 1228 and/or the storage controller 1230 may subscribeto certain types and amounts of services and resources provided by thedistributed computing platform 1202. For example, the client device 1228may establish a subscription to have access to three virtual machines, acertain amount of storage, a certain type/amount of data redundancy, acertain type/amount of data security, certain service level agreements(SLAs) and service level objectives (SLOs), latency guarantees,bandwidth guarantees, access to execute or host certain applications,etc. Similarly, the storage controller 1230 can establish a subscriptionto have access to certain services and resources of the distributedcomputing platform 1202.

As shown, a variety of clients, such as the client device 1228 and thestorage controller 1230, incorporating and/or incorporated into avariety of computing devices may communicate with the distributedcomputing platform 1202 through one or more networks, such as thenetwork 1226. For example, a client may incorporate and/or beincorporated into a client application (e.g., software) implemented atleast in part by one or more of the computing devices.

Examples of suitable computing devices include personal computers,server computers, desktop computers, nodes, storage servers, storagecontrollers, laptop computers, notebook computers, tablet computers orpersonal digital assistants (PDAs), smart phones, cell phones, andconsumer electronic devices incorporating one or more computing devicecomponents, such as one or more electronic processors, microprocessors,central processing units (CPU), or controllers. Examples of suitablenetworks include networks utilizing wired and/or wireless communicationtechnologies and networks operating in accordance with any suitablenetworking and/or communication protocol (e.g., the Internet). In usecases involving the delivery of customer support services, the computingdevices noted represent the endpoint of the customer support deliveryprocess, i.e., the consumer's device.

The distributed computing platform 1202, such as a multi-tenant businessdata processing platform or cloud computing environment, may includemultiple processing tiers, including the user interface tier 1204, theapplication server tier 1206, and a data storage tier 1208. The userinterface tier 1204 may maintain multiple user interfaces, includinggraphical user interfaces and/or web-based interfaces. The userinterfaces may include the service user interface 1210 for a service toprovide access to applications and data for a client (e.g., a “tenant”)of the service, as well as one or more user interfaces that have beenspecialized/customized in accordance with user specific requirements,which may be accessed via one or more APIs.

The service user interface 1210 may include components enabling a tenantto administer the tenant's participation in the functions andcapabilities provided by the distributed computing platform 1202, suchas accessing data, causing execution of specific data processingoperations, etc. Each processing tier may be implemented with a set ofcomputers, virtualized computing environments such as a storage virtualmachine or storage virtual server, and/or computer components includingcomputer servers and processors, and may perform various functions,methods, processes, or operations as determined by the execution of asoftware application or set of instructions.

The data storage tier 1208 may include one or more data stores, whichmay include the service data store 1220 and one or more client datastores. Each client data store may contain tenant-specific data that isused as part of providing a range of tenant-specific business andstorage services or functions, including but not limited to ERP, CRM,eCommerce, Human Resources management, payroll, storage services, etc.Data stores may be implemented with any suitable data storagetechnology, including structured query language (SQL) based relationaldatabase management systems (RDBMS), file systems hosted by operatingsystems, object storage, etc.

In accordance with one embodiment of the invention, the distributedcomputing platform 1202 may be a multi-tenant and service platformoperated by an entity in order to provide multiple tenants with a set ofbusiness related applications, data storage, and functionality. Theseapplications and functionality may include ones that a business uses tomanage various aspects of its operations. For example, the applicationsand functionality may include providing web-based access to businessinformation systems, thereby allowing a user with a browser and anInternet or intranet connection to view, enter, process, or modifycertain types of business information or any other type of information.

In an embodiment, the described methods and/or their equivalents may beimplemented with computer executable instructions. Thus, In anembodiment, a non-transitory computer readable/storage medium isconfigured with stored computer executable instructions of analgorithm/executable application that when executed by a machine(s)cause the machine(s) (and/or associated components) to perform themethod. Example machines include but are not limited to a processor, acomputer, a server operating in a cloud computing system, a serverconfigured in a Software as a Service (SaaS) architecture, a smartphone, and so on). In an embodiment, a computing device is implementedwith one or more executable algorithms that are configured to performany of the disclosed methods.

It will be appreciated that processes, architectures and/or proceduresdescribed herein can be implemented in hardware, firmware and/orsoftware. It will also be appreciated that the provisions set forthherein may apply to any type of special-purpose computer (e.g., filehost, storage server and/or storage serving appliance) and/orgeneral-purpose computer, including a standalone computer or portionthereof, embodied as or including a storage system. Moreover, theteachings herein can be configured to a variety of storage systemarchitectures including, but not limited to, a network-attached storageenvironment and/or a storage area network and disk assembly directlyattached to a client or host computer. Storage system should thereforebe taken broadly to include such arrangements in addition to anysubsystems configured to perform a storage function and associated withother equipment or systems.

In some embodiments, methods described and/or illustrated in thisdisclosure may be realized in whole or in part on computer-readablemedia. Computer readable media can include processor-executableinstructions configured to implement one or more of the methodspresented herein, and may include any mechanism for storing this datathat can be thereafter read by a computer system. Examples of computerreadable media include (hard) drives (e.g., accessible via networkattached storage (NAS)), Storage Area Networks (SAN), volatile andnon-volatile memory, such as read-only memory (ROM), random-accessmemory (RAM), electrically erasable programmable read-only memory(EEPROM) and/or flash memory, compact disk read only memory (CD-ROM)s,CD-Rs, compact disk re-writeable (CD-RW)s, DVDs, cassettes, magnetictape, magnetic disk storage, optical or non-optical data storage devicesand/or any other medium which can be used to store data.

Although the subject matter has been described in language specific tostructural features or methodological acts, it is to be understood thatthe subject matter defined in the appended claims is not necessarilylimited to the specific features or acts described above. Rather, thespecific features and acts described above are disclosed as exampleforms of implementing at least some of the claims.

Various operations of embodiments are provided herein. The order inwhich some or all of the operations are described should not beconstrued to imply that these operations are necessarily orderdependent. Alternative ordering will be appreciated given the benefit ofthis description. Further, it will be understood that not all operationsare necessarily present in each embodiment provided herein. Also, itwill be understood that not all operations are necessary in someembodiments.

Furthermore, the claimed subject matter is implemented as a method,apparatus, or article of manufacture using standard application orengineering techniques to produce software, firmware, hardware, or anycombination thereof to control a computer to implement the disclosedsubject matter. The term “article of manufacture” as used herein isintended to encompass a computer application accessible from anycomputer-readable device, carrier, or media. Of course, manymodifications may be made to this configuration without departing fromthe scope or spirit of the claimed subject matter.

As used in this application, the terms “component”, “module,” “system”,“interface”, and the like are generally intended to refer to acomputer-related entity, either hardware, a combination of hardware andsoftware, software, or software in execution. For example, a componentincludes a process running on a processor, a processor, an object, anexecutable, a thread of execution, an application, or a computer. By wayof illustration, both an application running on a controller and thecontroller can be a component. One or more components residing within aprocess or thread of execution and a component may be localized on onecomputer or distributed between two or more computers.

Moreover, “exemplary” is used herein to mean serving as an example,instance, illustration, etc., and not necessarily as advantageous. Asused in this application, “or” is intended to mean an inclusive “or”rather than an exclusive “or”. In addition, “a” and “an” as used in thisapplication are generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. Also, at least one of A and B and/or the like generally means A orB and/or both A and B. Furthermore, to the extent that “includes”,“having”, “has”, “with”, or variants thereof are used, such terms areintended to be inclusive in a manner similar to the term “comprising”.

Many modifications may be made to the instant disclosure withoutdeparting from the scope or spirit of the claimed subject matter. Unlessspecified otherwise, “first,” “second,” or the like are not intended toimply a temporal aspect, a spatial aspect, an ordering, etc. Rather,such terms are merely used as identifiers, names, etc. for features,elements, items, etc. For example, a first set of information and asecond set of information generally correspond to set of information Aand set of information B or two different or two identical sets ofinformation or the same set of information.

Also, although the disclosure has been shown and described with respectto one or more implementations, equivalent alterations and modificationswill occur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Thedisclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements, resources, etc.), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure. In addition, while aparticular feature of the disclosure may have been disclosed withrespect to only one of several implementations, such feature may becombined with one or more other features of the other implementations asmay be desired and advantageous for any given or particular application.

What is claimed is:
 1. A method comprising: performing a transitionoperation to transition a first storage object and a second storageobject from an asynchronous replication state to a synchronousreplication state; synchronizing the first storage object and the secondstorage object during the transition operation; and replicating a holereservation flag of an operation targeting the first storage object intoa replication operation targeting the second storage object during thetransition operation, wherein the hole reservation flag is set toindicate that a persistent hole reservation is enabled to reservestorage space that is to be written to by the operation.
 2. The methodof claim 1, comprising: modifying a punch hole operation to set acorresponding hole reservation flag on an inode.
 3. The method of claim1, comprising: performing a reconciliation operation based uponexecution of the replication operation succeeding upon the secondstorage object and execution of the operation failing upon the firststorage object.
 4. The method of claim 3, wherein hole reservation flagsof operations targeting the first storage object are replicated withinreplication operations targeting the second storage object during thereconciliation operation.
 5. The method of claim 1, comprising:determining that a replication punch hole operation failed due totargeting a file block number of the second storage object that isgreater than an end of size of the second storage object.
 6. The methodof claim 5, comprising: transmitting a write operation to the file blocknumber for the second storage object as specified by the replicationpunch hole operation to increase a size of the second storage object. 7.The method of claim 6, comprising: re-issuing the replication punch holeoperation to the second storage object based upon the write operationcompleting.
 8. The method of claim 1, comprising: tracking dirty regionsof the first storage object that are modified by operations during thetransition operation using a dirty region log.
 9. The method of claim 8,comprising: replicating the dirty regions to the second storage objectduring the transition operation.
 10. The method of claim 9, comprising:performing a dirty region read to replicate data of a dirty region tothe second storage object, wherein the dirty region read evaluates aninode associated with the dirty region to determine whether acorresponding hole reservation flag is set.
 11. The method of claim 10,comprising: replicating the data of the dirty region and thecorresponding hole reservation flag to the second storage object basedupon the corresponding hole reservation flag being set.
 12. Anon-transitory machine readable medium comprising instructions forperforming a method, which when executed by a machine, causes themachine to: perform a transition operation to transition a first storageobject and a second storage object from an asynchronous replicationstate to a synchronous replication state; synchronize the first storageobject and the second storage object during the transition operation;and replicate a hole reservation flag of an operation targeting thefirst storage object into a replication operation targeting the secondstorage object during the transition operation, wherein the holereservation flag is set to indicate that a persistent hole reservationis enabled to reserve storage space that is to be written to by theoperation, and wherein the hole reservation flag causes a reservation ofcorresponding storage space within the second storage object.
 13. Thenon-transitory machine readable medium of claim 12, wherein theinstructions cause the machine to: determine that a replication punchhole operation failed due to targeting a file block number of the secondstorage object that is greater than an end of size of the second storageobject.
 14. The non-transitory machine readable medium of claim 13,wherein the instructions cause the machine to: transmit a writeoperation to the file block number for the second storage object asspecified by the replication punch hole operation to increase a size ofthe second storage object.
 15. The non-transitory machine readablemedium of claim 14, wherein the instructions cause the machine to:re-issue the replication punch hole operation to the second storageobject based upon the write operation completing.
 16. A computing devicecomprising: a memory comprising machine executable code for performing amethod; and a processor coupled to the memory, the processor configuredto execute the machine executable code to cause the processor to:perform a transition operation to transition a first storage object anda second storage object from an asynchronous replication state to asynchronous replication state; synchronize the first storage object andthe second storage object during the transition operation; and replicatea hole reservation flag of an operation targeting the first storageobject into a replication operation targeting the second storage objectduring the transition operation, wherein the hole reservation flag isset to indicate that a persistent hole reservation is enabled to reservestorage space that is to be written to by the operation.
 17. Thecomputing device of claim 16, wherein the machine executable code causesthe processor to: track dirty regions of the first storage object thatare modified by operations during the transition operation using a dirtyregion log.
 18. The computing device of claim 17, wherein the machineexecutable code causes the processor to: replicate the dirty regions tothe second storage object during the transition operation.
 19. Thecomputing device of claim 18, wherein the machine executable code causesthe processor to: perform a dirty region read to replicate data of adirty region to the second storage object, wherein the dirty region readevaluates an inode associated with the dirty region to determine whethera corresponding hole reservation flag is set.
 20. The computing deviceof claim 19, wherein the machine executable code causes the processorto: replicate the data of the dirty region and the hole reservation flagto the second storage object based upon the corresponding holereservation flag being set.